Elastic collision with pendulum

1. The problem statement, all variables and given/known data
A steel ball of mass 0.890 kg is fastened to a cord that is 50.0 cm long and fixed at the far end. The ball is then released when the cord is horizontal, as shown in the figure. At the bottom of its path, the ball strikes a 2.50 kg steel block initially at rest on a frictionless surface. The collision is elastic. Find (a) the speed of the ball and (b) the speed of the block, both just after the collision.

2. Relevant equations

3. The attempt at a solution
So first found the velocity of the ball just before it collided with the block:
V=(2*g*L*(1-cosΘ))^0.5
V=(2*9.81*0.5*(1-cos45))^0.5
V=2.873 m/s

So then I used that to find the velocity of the block using elastic collision formulas:
V2f= (2*m1)/(m1+m2)*V1i
= (2*0.89)/(0.89+2.5)*2.873
=1.51 m/s

And then for the velocity of the ball following the collision:
V1f=(m1-m2)/(m1+m2)*V1i
=(0.89-2.5)/(0.89+2.5) * 2.873
=-1.37 m/s

I used these solutions (the absolute value of the vel of the ball as it asked for speed) and that was incorrect.
Now I did try and double check myself and found that with these numbers momentum is conserved so what am I missing here?